Iran on Saturday summoned the British ambassador to Tehran, the foreign ministry said, hours after a British-Iranian dual national was executed for espionage.

Former senior defence official Alireza Akbari, 61, was hanged after being convicted of "corruption on earth and harming the country's internal and external security by passing on intelligence", Iran judiciary's Mizan Online website said. 

It did not say when it happened. However, there were rumours he had been executed days ago.

Mizan said Akbari, who had been arrested more than two years ago, had been a spy for Britain's MI6 secret intelligence agency and had received around $2 million for his services.

"In response to Britain's unconventional interventions, including in the national security field of the Islamic Republic of Iran, today, Simon Shercliff, the ambassador of this country in Tehran, was summoned," the ministry said in a statement.

"In this meeting, our country's protest against the acts of sabotage and acts against (Iran's) national security was reflected to the British government," it added.

The statement stressed "the British government should be held accountable for establishing unconventional communications leading to an attack on (Iran's) national security."

"The continuation of such illegal and criminal actions cannot be tolerated in any way; therefore, the British government must accept the consequences of the responsibility of continuing its unorthodox and interventionist approach."

Iran does not recognise dual nationality for its citizens.

Earlier, Prime Minister Rishi Sunak said he was "appalled", adding: "This was a callous and cowardly act, carried out by a barbaric regime with no respect for the human rights of their own people."

Britain said the "barbaric" hanging of Akbari, would not go unchallenged.

"This barbaric act deserves condemnation in the strongest possible terms. This will not stand unchallenged," Foreign Secretary James Cleverly said.

On Thursday, state media had reported that 61-year-old Akbari had held high positions in the country's defence establishment.

His posts included "deputy minister of defence for foreign affairs" and a position in the "secretariat of the Supreme National Security Council."

Akbari had also been an "advisor to the commander of the navy" as well as "heading a division at the defence ministry's research centre".

In a video published by Iranian media, Akbari is seen apparently talking about his contacts with Britain.

He also says he was questioned by the British about Iran's top nuclear scientist Mohsen Fakhrizadeh, assassinated in November 2020 in an attack that Tehran blames on arch-foe Israel.

Akbari, a veteran of the Iran-Iraq war that raged from 1980-1988, was arrested sometime between March 2019 and March 2020, state media said.

Mizan, citing a statement from Iran's intelligence ministry, had said earlier this week that Akbari became a "key spy" for Britain's Secret Intelligence Service, more commonly known as MI6, due to "the importance of his position".

In February 2019, the official government newspaper Iran published an interview with Akbari, whom it identified as a "former deputy defence minister" during the 1997-2005 presidency of Mohammad Khatami.

In early December, Iran executed four people accused of working with Israeli intelligence, Mizan said at the time.

Iran hanged them four days after the Supreme Court upheld their death sentence for "their intelligence cooperation with the Zionist regime (Israel) and kidnapping", Mizan reported.